Thrombin related peptide (TP 508) is a 23 amino-acid synthetic peptide that mimics a portion of the receptor-binding domain of the human thrombin molecule.

Thrombin triggers both proteolytic activated receptors and non proteolytic activated receptors to bring about a mixture of responses ranging from tissue breakdown and clot formation, to new vessel formation and tissue repair. TP 508 stimulates only the non proteolytic activated receptors, and this initiates repair and angiogenesis but not clot formation or tissue breakdown Previous studies have shown that TP508 can stimulate repair in the dermal and musculoskeletal tissues by promoting angiogenesis and enhancing the proliferation and migration of cells.

High energy fractures are associated with a delay in healing. We hypothesized that high energy fracture healing would be improved with the use of TP508, and that the dose and site of application would have importance.

Methods: 80 CD 1 Mice were randomised into four groups; all underwent a high energy quadriceps muscle crush and a femoral fracture on the left hind limb. In each case the fracture was reduced and held with an external fixator. At the time of operation Group I received a dose of 100ìg TP 508 into the fracture, Group II 100ìg into the surrounding damaged soft tissue, Group III a dose of 10ìg into the fracture, and group IV (the control group) received PBS carrier into the fracture.

24 animals were sacrificed on day 21 and the remaining 56 mice on day 35. Of the 35 day old animals 8 in each group had both femora harvested and the biomechanical properties were tested using the 3-point bending technique. Specimens from the 21 day old animals and remaining 35 day old animals were used for histological analysis.

All 80 animals had digital radiographs taken each week. Using image analysis software five pixel density graphs were generated across each fracture gap. A validated semi quantitative analysis was used to score each graph and the total accumulated for each radiograph. The width of the fracture calus was measured and expressed as a ratio of the femur diameter.

Results: Mechanical testing showed significantly greater stiffness in group I when compared to control (p < 0.05), and a dose dependent trend of increasing strength.

Radiographic analysis showed greater healing of fracture and callus formation in Group I compared to Groups II, III, and IV, at both three and five weeks post-fracture (P< 0.05).

Histological analysis showed an increase in bone formation in group I compared to the other groups.

Conclusion: This data from this model, suggests that TP508 enhances healing in high energy fractures. The results also suggest that the effects of TP508 are dose dependant, and are greater when delivered into the fracture site.